html{
    display: flex;
}
body{
    display: flex;
}
#video1{
    position: absolute;
    top:50%;
    left:50%;
    border-radius: 5px;
    -webkit-transform: translate(-50%,-50%);
    -moz-transform: translate(-50%,-50%);
    transform:translate(-50%,-50%);
}